In a fuel battery, a fuel battery cell serving as a single cell is constituted by a membrane-electrode assembly (MEA) comprising an electrolyte layer, such as a solid polymer membrane and diffusion layers of carbon cloth or carbon paper holding the electrolyte layer therebetween, and of separator members holding the membrane-electrode assembly therebetween, and a plurality of such cells are arranged or stacked (modularized) to construct a fuel battery. In such a single fuel battery cell, a hydrogen gas as an anode gas is supplied to a hydrogen gas flow channel groove of the negative side separator, and air (oxygen gas) as a cathode gas is supplied to an oxygen gas flow channel groove of the positive side separator. The supplied hydrogen gas and oxygen gas are diffused to a negative side diffusion layer and a positive side diffusion layer, respectively. The hydrogen gas which has reached the negative side diffusion layer then contacts a catalyst layer applied onto the solid polymer electrolyte membrane, and is dissociated into charged protons and electrons. The dissociated protons pass through the solid polymer membrane, move to a positive side, and react with the oxygen on the positive side to form water, thereby generating electricity. In general, a plurality of single cells having such a power generation mechanism is used and stacked via separators, such that the assembled fuel battery is constructed as a series-connected cell module or cell stack.
In order to bond the single cells of the fuel battery, a liquid adhesive is used, and the single cells of the fuel battery are joined by this adhesive. First, the liquid adhesive is applied onto a joint surface of one separator member. The applied adhesive is solidified by thermal hardening after the joint surface of this separator member is covered with an adjacent member. In this manner, the separator can be joined to the adjacent member by the adhesive. This liquid adhesive must be applied onto the joint surface (at least the entire outer peripheral edge) of the separator member because if any places, even small locations, remain where the adhesive is not applied, the gas flowing in the fuel battery may leak from the places where the adhesive is not applied when the separator is joined to the adjacent member. To prevent this, it is therefore necessary to adequately apply the adhesive to the separator member. That is, the adhesive has a function as a seal member.
The adhesive is preferably applied onto the joint surface (at least the entire outer peripheral edge) of the separator member as adequately as possible, but application of too much adhesive may lead to other problems. That is, if the thickness of the adhesive applied onto the entire the joint surface of the separator member is not uniform and there are places where the thickness of the applied liquid adhesive varies, surface pressure distribution may vary when the separator member is joined. For example, such a variation in the surface pressure distribution weakens the adhesion force between the MEA and the separator member by the adhesive, or increases the degree of electric loss (an increase in contact resistance) in the fuel battery. Moreover, between the separator member and the MEA, there is a possibility that the gas flow channels provided in the separator member may deform such that the gases will not flow along the designed flow channels.
A technique is known which, in view of such problems with the adhesive application amount and the surface pressure distribution, crosses a leading end and a terminal end when applying the liquid adhesive. At this point, it is considered that the separator member is preferably provided with a wide portion in a part where the leading end is joined to the terminal end.
Meanwhile, in the separator member onto which the adhesive is applied, a place where the application amount of the adhesive is great is first compacted, and then other portions with the adhesive are compacted such that the separator member is bonded to the adjacent member, when the separator member is bonded (sealed) with the adhesive to the adjacent member (e.g., the electrolyte membrane, the separator, a resin frame, etc.) opposite to the separator member in a cell stacking direction. Especially at a cross portion of the adhesive, the adhesive is applied so as to be superposed in two or more layers, which tends to create a bulky state.
At this point during assembly, because the surface pressure in such a bulky cross portion becomes higher than in other portions, the compacted adhesive spreads over the periphery of the cross portion. Especially, depending on the condition when the separator member is joined to the adjacent member with the adhesive, the direction and amount in which the compacted adhesive spreads out can vary.
A conventional separator member is provided with a wide portion at portions where the leading end crosses the terminal end. However, when the compacted adhesive disproportionately spreads within the space of the wide portion depending on the condition during the joining, the adhesive in some cases runs over from the wide portion in an arbitrary direction.
Such overflowing adhesive might, for example, enter and block the gas flow channels or a cooling fluid flow channel of the separator, or hamper the function of the MEA. Further, when the adhesive runs over into a manifold for the gas flow channels and the cooling fluid flow channel formed in the separator member, the adhesive hampers the flow of the gases or a cooling fluid. Moreover, when there is a possibility that the adhesive may overflow into the manifold, it may be necessary to include in the manufacturing process an additional process for removing the run-over adhesive. In addition, there is a possibility that deviation in the wide portion will lead to variations in the application amount (surface pressure) and impair the sealing function.
The present invention was made in view the above problems, and provides a separator of a fuel battery having a more suitable bonded structure and a fuel battery using this separator.